O Level / IGCSE Biology chapter 17: Inheritance MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
45 exam-style questions on Inheritance, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. What must exist within a population for natural selection to take place?
A
identical individuals with the same alleles
B
an unlimited supply of food and water
C
variation between the individuals
D
no predators or competitors in the habitat
Show answer
Answer: C. Selection can only act if individuals differ; some variants survive and reproduce better than others.
2. What is each strand of a DNA molecule made of?
A
a chain of amino acids
B
a chain of glucose molecules
C
a chain of fatty acids
D
a chain of nucleotides
Show answer
Answer: D. Each strand is a chain of nucleotides, and each nucleotide contains one base.
3. What causes continuous variation such as body mass?
A
mutation only, in the cells of the muscles and fat
B
the environment only, such as diet and exercise
C
genes only, because mass is inherited from the parents
D
genes and the environment together
Show answer
Answer: D. Many genes plus environmental factors such as diet and exercise combine to give a range of values.
4. Why do different proteins have different shapes?
A
they are made in different organs of the body
B
they contain different numbers of bases in a strand
C
they are built from different types of sugar
D
their amino acid sequences differ
Show answer
Answer: D. The amino acid sequence determines how a protein folds, and so its shape and function, such as the shape of an enzyme's active site.
5. What is variation?
A
the number of different species living in an area
B
differences between the species living in one habitat
C
differences between individuals of one species
D
changes in the environment over long periods of time
Show answer
Answer: C. Variation means individuals of one species differ from one another.
6. Which feature of pea plants shows discontinuous variation?
A
total leaf area of each plant, in square centimetres
B
mass of the seeds from each plant, in grams
C
length of the pods, measured in centimetres
D
seed shape, round or wrinkled
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Answer: D. Seed shape has two clear categories with no intermediates. Mass, length and area vary continuously.
7. What are pure-breeding organisms?
A
heterozygous, so their offspring show variation
B
homozygous, so all their offspring are the same
C
organisms that have a mutation in one of their genes
D
organisms that reproduce only asexually by cloning
Show answer
Answer: B. Two identical homozygous parents can only pass on one type of allele, so all their offspring are the same.
8. A pair of rabbits can produce over 20 young in a year, yet the rabbit population in an area stays about the same over many years. What is the main reason?
A
most of the young rabbits are sterile and never reproduce
B
more young are born than the environment can support, so many die
C
all the young are identical, so one disease kills them together
D
rabbits stop reproducing as soon as the population becomes large
Show answer
Answer: B. Over-production leads to a struggle for survival through competition, predation and disease; only some offspring live to reproduce, which is the basis of natural selection.
9. Which factor increases the rate of mutation?
A
a balanced diet rich in vitamins and minerals
B
exposure to ionising radiation
C
regular exercise for at least an hour a day
D
drinking plenty of water in hot weather
Show answer
Answer: B. Ionising radiation, such as X-rays and gamma rays, and some chemicals increase the rate of mutation.
10. A cross between two pea plants produces 62 tall and 58 short offspring. Tall (T) is dominant to short (t). Which parents most likely produced these offspring?
A
a heterozygous tall parent and a short parent
B
two heterozygous tall parents
C
a homozygous tall parent and a short parent
D
a homozygous tall parent and a heterozygous tall parent
Show answer
Answer: A. Short offspring (tt) need a t allele from each parent, so both parents carry t. A 1 : 1 ratio comes from a heterozygous tall parent (Tt) crossed with a short parent (tt). Tt × Tt would give about 3 tall : 1 short, and TT × tt would give all tall.
45, each with the answer and a short explanation, across 4 topics: Variation, DNA, Inheritance, Selection. Every chapter test draws ten of them, so you can take it many times.
Is the O Level / IGCSE Biology chapter 17 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
